I Have a Higher Loyalty, Says McClellan

Before it's even been put on the shelves, Scott McClellan's blistering look at the Bush administration has zoomed to the top of Amazon.com's best-seller list.

Confronted with attacks by current and former Bush administration officials, the one time White House spokesman defended his decision to attack his old boss and his colleagues in the White House, where loyalty to the president was considered a prime qualification for employment.

"No one questioned my loyalty to the president when I was there," McClellan told ABC News White House Correspondent Martha Raddatz during an interview Thursday.

"But there's a higher loyalty, there's a higher loyalty to the truth, it's a loyalty to the values I was raised upon which are speaking up, which are making a positive difference," he said.

Watch part of Martha Raddatz's interview with Scott McClellan on ABC World News Thursday at 6:30pmET.

For the full transcript of McClellan's interview with Martha Raddatz click HERE.

Even political insiders were unaware that McClellan's White House memoir, "What Happened, " was in the works until news about it broke Wednesday morning. Nevertheless, by this morning it had shot to the top of Amazon.com's best-seller list.

The controversial tome accuses the Bush administration of being "evasive" and "shading the truth" on a range of issues including the administration's motivations for going to war in Iraq. He said administration officials exaggerated the threat posed by Saddam Hussein and ignored intelligence that portrayed a different picture.

Speaking publicly since the storm over his book erupted Wednesday, the former press secretary told ABC News he became swept up in his role as a spokesperson and advocate for the President of the United States.

When asked about his role as a public servant, McClellan said, "You serve the public, but you also serve the president of the United States," he said. "That was my job, it was my job to be the advocate and spokesman for the President of the United States."

"I fell short in terms of myself, fullfilling my duties as a public servant in many ways at different times throughout the administration but at the time, I was so caught up -- you're so caught up in the White House bubble." McClellan said.

He said, however, that the realization that he had been used to promote the administration's "propaganda" led him to speak out.

" I was sincere about what I was saying at the time. But like others I got caught up in this whole Washington atmosphere too," he said.

McClellan said that he did not write the book to make money and knew he was alienating many of his friends, but that he was moved to detail behind-the-scenes White House maneuvers because he was brought up to know the importance of speaking up and making a positive difference.

"When you get inside that bubble, you have great affection for the person you're serving, you have all these high hopes that you're coming to Washington and he's sincere about bringing this bipartisan spirit and that we're going to change things. And then over time you realize that what you pledged to change, you became," McClellen told Raddatz.

McClellan has been be assailed by a who's who of current and former administration officials, who question his loyalty, his access to information and motives for speaking now and not, they caustically note, when he was working in the White House.